Chevy Big Block "Rat" Engine Upgrades

When the discussion turns to making big power affordably, the Chevrolet big-block "Rat" engine has few peers. Although it was one of the longest running production passenger car powerplants, it was designed from the get-go with on-track ability in mind. Chevrolet seriously stepped up the engine program in comparison to the previous generation of W-series big-blocks with an eye toward racing. The key step here was the Rat's "Porcupine" cylinder head layout, featuring the architecture to accommodate massive ports, steep valve cant angles, and a simple but very capable stud-mounted rocker arrangement. Where man-sized helpings of horsepower are on order, the big-block Chevy is ready to serve it up.

Today, the big-block Chevy is still the foundation for massive power in a readily available package. The aftermarket has expanded on Chevrolet's original concept, with race-ready parts to build these engines in virtually any configuration imaginable. Eric Weingartner of Weingartner Racing looked no further than the big-block Chevy platform when considering an engine combination for the 2013 AMSOIL Engine Masters Challenge (EMC).

2/18To serve as a foundation, Eric Weingartner started with a Dart block. The aftermarket block offers far bigger bore potential than any stock big-block, and swallows long stroke crankshafts with ease. The Scat crank provides 4.250 inches of stroke.

Big Bottom End

Weingartner had run big-block Chevy combinations at the EMC in prior years, and tells us, "I wanted to do something with what I already had, and I already had a big-block. I ran a big-block 496 big in a previous competition, and I wanted to take another stab at it. I knew it wouldn't be competitive in the event due to the size of it, but the goal was to make as much power as possible on pump gas. I had the Dart Big M block sitting over here complete with a rotating assembly that I bought two years ago, but I never did anything with it."

Although a production-based big-block Chevy can be modified to achieve substantial cubic-inch capacity, the big-bore aftermarket ups the ante significantly. The Dart Big M block can easily accommodate a 4.500-inch bore, and has the crankcase capacity to greatly exceed the production stroke. Most importantly, the block is built with the beefed-up structure to keep all those cubes in one piece. Weingartner's final configuration of a 4.500-inch bore and 4.250-inch stroke brought the cubic capacity to a healthy 540 ci, which is far from the maximum capability of the block. Weingartner's new engine would essentially be a bigger bore version of the popular production-based 496 combo. Weingartner explains: "With the nice long stroke, the bigger bore will unshroud the valves better than the smaller bore 496 combo."

Starting with a high-performance aftermarket block, few modifications were necessary for the block. As Weingartner relates, "There really was nothing fancy done on the block itself. It retains the bolts and parts as it comes from Dart. These blocks are said to handle 1,200 hp, and I knew this application would not be anywhere close to that, so the strength was already there. The block already had sufficient clearance for the 4.250-inch stroke crank, so that part was virtually a drop in. I went with the standard-weight Scat 4.250-inch stroke crank instead of the lightweight version, since the lighter crank can't take as much power, so it left more in the bank for reliability. Andy Key, a former Engine Masters competitor, helped me with the machine work. About the only custom work to the block was that the lifter bores were bushed and enlarged to 0.904 inch."

3/18Billet steel four-bolt splayed main caps are a production feature of the Dart Big M block, adding substantially to bottom-end strength. Weingartner tells us the main hardware as supplied by Dart is more than up to the task.

Weingartner's parts stash included a set of off-the-shelf 39cc dome MAHLE pistons which he modified for use in this engine: "I had the high-compression MAHLE pistons, and thankfully they had a solid dome, so I had the domes milled to get the compression ratio down to 11.5:1, and added the lateral gas ports. The rings are the gapless type from Total Seal. Part of that choice is due to anticipating nitrous on this engine after the Engine Masters Challenge. At the event you want the gap kind of narrow, but with the gapless top rings we could set the gaps wider and they will be fine. If the big-block has one drawback, it is the really big combustion chamber. You have to run a dome in it, which makes the flame travel process difficult without hampering the torque production per cubic inch."

Linking the modified pistons to the rods is a set of Scat 6.325-inch H-beam connecting rods. Weingartner tells us, "The H-beam rods are very strong, but I did upgrade the bolts to the ARP 2000 capscrews. For this application it was probably not necessary, but the upgrade gives more rpm capacity in case I ever wanted to spin it to a higher rpm in the future—plus it is added security."

The revised lubrication circuit of the Dart block alleviated the need for major oiling system modifications, though the oil pump selection did require attention. Weingartner detailed his experience, "We started with a standard-volume replacement pump, but at the top end of the pulls we saw the oil pressure start dropping off. We went back to the dyno with a Titan oil pump, and the Titan pump sure fixed it. It was just the standard volume Titan, and the oil pressure is set kind of low, but the oil pressure barely fluctuated. That Titan pump is nice." Completing the lubrication system is a Hamburger oil pan, featuring a built-in windage screen and baffles. As Weingartner tells, "It is a nice piece that bolted right on, and it does the job."

Working Top End

Of course all of the cubic inches you can pack into an engine combination will not do any good if the top end components are not up to the task of feeding them. Weingartner's specialty is cylinder head development, so this aspect of the build received the bulk of the attention. As Weingartner tells us, "The heads are the RHS 320s. I started out with a CNC program from a previous combination that had the intake ports at about 335 cc, and from there I ground them bigger and then added a ton of epoxy to the floor. The heads ended up at about 348cc total intake volume, and flowed 442 cfm. The valve combination is a 2.300-inch intake and a 1.88-inch exhaust valve. I would have liked to have gone with a bigger intake valve, but the seats weren't big enough to run the 2.350-inch size I wanted. I did not want to cut the seat inserts out to do it. When all the modifications were completed, all the runners flowed very close to the same. The short ones were down about 10-15 cfm at the very peak, but up until the top they were right there; it was pretty tight. The exhaust with a pipe was at 345 cfm."

11/18On the dyno at the 2013 AMSOIL Engine Masters Challenge we had the opportunity to see this engine in action. With 852 hp on tap and 759 lb-ft of torque, this straightforward big-block was big on power.

Weingartner continued, "The manifold is the Edelbrock 2896 Super Victor. It has more epoxy in it than both heads combined. When I added the epoxy to the floor of the heads, it raised the runners, so I had to do the same to the intake to match it. I also raised the floor of the plenum to shrink the plenum volume, and once it was shrunk down, it worked pretty well. I flow tested all the runners, and with the intake attached as well as the carb, they all flowed at least 400 cfm. I was pretty happy with that. The runners were all very consistent."

Cam and Valvetrain

Creating a functional engine combination requires that the camshaft and valvetrain work in harmony with the rest of the engine configuration, and here Weingartner shares his experience: "The camshaft is actually by Chris Straub at Straub Technologies. I had my own specs in mind and tried another cam, and mine just wasn't as good. The cam from Chris was ground by Bullet to his specs, and it made about the same power as mine, but it made more torque. His lobes were not quite as aggressive as mine, and I thought that would lose power, but it didn't. The cam specs ended up at .801/.834 with 260/270 duration at .050, and a 107-degree lobe separation installed at 103.5. Chris also supplied the Morel hydraulic .904-inch lifters for a big-block Chevy. These lifters are really nice and very strong. It is not limited travel, but it will take a lot of spring pressure. I ran them with 275/800 pounds of spring load, and they held up great."

In conjunction with the cam, the valvetrain has to consist of components compatible with the task on hand. Here Weingartner zeroed in on a functional setup through testing on the dyno. "I tried different springs, starting with a 1.625-inch spring and switched over to a 1.55-inch spring with the same pressure. The smaller spring made the valvetrain more stable at higher rpm. I also swapped from aluminum rockers to the COMP Ultra Pro Magnum steel rockers. From measuring with and without the checking springs I found the aluminum rockers had more lift with the checking springs, but with the real springs the steel rockers had more lift. This was because of deflection with the aluminum rockers. The steel rockers didn't deflect as much and delivered more lift. I think that they probably make more power because of that. I used the RHS stud girdle and also went with the ARP 2000 rocker arm studs just to be safe and make sure nothing would break. The valvetrain was very stable after getting the springs figured out, working flawlessly to well past 7,000 rpm.

12/18The Morel hydraulic lifters are special .904-inch diameter units for the big-block Chevy application. Though these lifters feature full plunger travel, they worked flawlessly with spring loads topping 800 pounds.

Finishing Touches

Although an engine of this size would normally benefit from a large 4500-Series Dominator-style carb, for the EMC competition the rules limited the competitors to a single 4150-style carb. Here Weingartner again relied upon dyno testing to optimize the engine under the build constraints. "I used a Braswell 4150, although I also tried another carb that actually made a little more power, I couldn't get it rich enough no matter how much jet I added. The metering inside the carb was just maxed out, and I didn't want to tear up the motor by running it too lean. The Braswell was able to keep up with the fuel requirement at this power level."

Lighting the mixture is an ignition from Australian manufacturer ICE, working in conjunction with an MSD crank trigger. As Weingartner observed, "I ran the ICE ignition with the crank trigger, but I actually tried it both ways—with the crank trigger and without it. You can easily switch back and forth by just unplugging the cable from the trigger and hooking it to the distributor, and it turns out I didn't see a power benefit. It did keep the timing more stable, so that is a plus with the crank trigger. Also, if we had to swap the intake manifold we didn't have to worry about resetting the timing, so that is an advantage."

Makin' Power

We had a chance to see Weingartner's big-block in action against the SuperFlow Powermark dyno at the 2013 AMSOIL Engine Masters Challenge, where in terms of raw power, the engine was among the leaders. Certainly from a dollar-per-horsepower perspective, it was at the top of the heap. Here we had a powerplant that embodied the potential of a conventional big-block Chevy with everyday parts—essentially, it was a traditional hot rodded big-block. From its factory deck height block, to the OEM layout replacement heads, as well as the single four-barrel 4150 induction, this engine resembles everyman's hot street big-block.

Where this engine really separated itself from the pack was the sheer twist and pull against the dyno's brake. Right at the hit we witnessed 634 lb-ft of uncontrollable torque, rising steadily to a peak of 759 lb-ft at 5,400 rpm. That torturous torque will twist a stock Camaro in half. Powering up to a peak of 852 hp at 6,600-6,700 rpm, the top end punch is right in the sweet spot for a knockout blow on the street. Chevrolet engineered the potential for this kind of power decades ago, and performance engine builders like Weingartner Racing have been making the most of it ever since.

13/18A peek inside the intake shows the epoxy filling done to the floor of the manifold, which extends to the plenum floor. Note the rough carbide finish on the runner walls.

On The Dyno 540ci Big-Block Chevy

RPM

TQ

HP

3,000

634

362

3,100

630

372

3,200

611

372

3,300

578

363

3,400

565

365

3,500

579

386

3,600

601

412

3,700

625

441

3,800

649

469

3,900

669

496

4,000

687

523

4,100

697

544

4,200

711

569

4,300

721

590

4,400

727

609

4,500

732

628

4,600

739

647

4,700

746

667

4,800

751

686

4,900

753

702

5,000

754

718

5,100

755

733

5,200

757

750

5,300

758

765

5,400

759

781

5,500

758

794

5,600

757

807

5,700

752

816

5,800

747

825

5,900

741

833

6,000

732

836

6,100

725

842

6,200

717

847

6,300

709

850

6,400

697

849

6,500

687

850

6,600

678

852

6,700

668

852

6,800

654

847

6,900

641

842

7,000

627

836

By The Numbers 540ci Chevy Big-Block

Bore:

4.500 inches

Stroke:

4.250 inches

Displacement

540 ci

Compression ratio:

11.5:1

Camshaft:

custom Straub Technologies hydraulic roller

Valve lift:

.801/.834 inch

Rocker and ratio:

COMP Cams 1.8/1.7:1

Piston rings:

Total Seal 1.5/1.5/3mm

Piston:

MAHLE forged

Block:

Dart

Crankshaft:

Scat forged

Rods:

Scat 6.385 inches

Cylinder head:

RHS 320 cc

Intake valve diameter:

2.300 inches

Exhaust valve diameter:

1.88 inches

Intake manifold:

Edelbrock

Carb:

Braswell 4150

Header:

Hedman 2-inch primary

Ignition:

ICE/MSD

Damper:

Powerbond

Oil Pan:

Hamburger

Fuel:

VP 100 Unleaded

Oil:

AMSOIL

14/18Eric Weingartner (right) was assisted by team member Greg Palmer at the 2013 AMSOIL Engine Masters Challenge, but noted that the effort would have been impossible without the additional support of his wife, Kerry; son, Bishop; Donney and Andy Key; and Dunsworth Machine.

18/18An ignition system from Australian manufacturer ICE provided the spark, assisted by an MSD crank trigger. The high energy of this system proved flawless in competition.